"There were some things that were said and done at the crime that the witness has told us that leads us strongly to believe that it was gang-related," said Chief Cecil Rhambo of the L.A. County Sheriff's department.
Farber, who was set to graduate next month and was planning to attend Harbor College, was a standout football player at Narbonne.
Dozens of people gathered outside the restaurant Monday night for a candlelight vigil in Farber's memory.
"This was a young man that definitely was an example of what we can mimic ourselves as far as his integrity, his diligence, his dedication," said Farber's cousin Mark Miller.
Anyone with information about the murder is asked to call L.A. County Sheriff's homicide detectives Toni Martinez or Eddie Brown at (323) 890-5500.